1. Field of the Invention
This invention relates to lifting tape off of a rotating head when the rotating head is not being used to read or write information on the tape.
2. Problem Background
In tape recorders using rotating heads one of the biggest technical problems is head and tape wear. The relative velocity between head and tape in a rotating head tape recorder is quite high, usually in the order of 1000 inches per second. At these speeds, contact between head and tape can damage heads and destroy tape in a matter of seconds.
To obviate this problem, rotating head recorders have utilized heads of particularly hard surface characteristics to resist wear, or alternatively, have designed heads that will fly within a few microinches of the surface of the tape. One example of a flying rotating head is described in copending commonly assigned application Ser. No. 486,028, filed July 5, 1974 and entitled "Slotted Rotating Head Which Flies Relative to Flexible Magnetic Media." The flying head is particularly effective to increase the longevity of the head and minimize wear on the tape.
The life of a flying head can be extended further by lifting the tape away from the flying head except during read/write operations. The flying height being on the order of tens of microinches creates an environment for the head that is susceptible to head crash damaging. Crashes between the flying head and the tape might occur because of debris getting between the head and the tape or other transient conditions. Therefore, it is desirable to lift the tape away from the head even further than the flying distance when the head is not reading or writing information on the tape.
Lifting the tape away from the head might be accomplished by using mechanical fingers as in U.S. Pat. No. 3,564,158. The difficulty with such a mechanical tape lifter is that the mechanical fingers are engaging the oxide surface of the tape. As the tape moves, the magnetic oxide can be damaged by the fingers and create debris that can subsequently cause a flying head to crash into the tape during read/write operations. Thus in very low flying heights, with high speed rotating heads, the mechanical fingers do not solve the problem of lifting the tape away from the head when the head is not being used to read or write.
An alternative solution to the mechanical fingers would be pneumatics on the rotor and/or mandrel to provide high air pressure to blow the tape away from the path of the rotating head. In other words, the entire length of tape wrapping the head could be pneumatically lifted away from the rotor. While this would definitly extend the life of the head, this alternative has at least two associated problems. First, a separate pneumatic system having a pressure several psi higher than an air bearing pneumatic system would have to be provided. Such an additional pneumatic system would be costly. Second, to lift the tape along the entire path of the rotating head would add delay in switching from a non-read/write operation to a read/write operation. In other words, in a non-read/write operation the tape would be lifted a relatively large distance off of the entire rotor and possibly the entire mandrel. When a read/write operation were desired, the thick air bearing during tape lift between the tape and mandrel would have to be collapsed and transient conditions in the tape would have to settle out before the head would fly at the very low flying height necessary for read/write operation. This collapse of the high air bearing and settling of transients would create a significant delay time in starting read/write operations with the tape drive.